Pipette

ABSTRACT

A pipette capable of accurately picking up, mixing and dispensing liquids in predetermined ratios without instrument calibration is disclosed. The pipette apparatus has cooperable shoulder means for accurately regulating relative movement of the pipette plunger means and casing to permit the sequential and separate pick up of different liquids, the mixing of the different liquids within the apparatus and the dispensing of the mixed liquids from the apparatus.

FIELD OF THE INVENTION

The present invention relates to pipette apparatus and, moreparticularly, to apparatus which accurately picks up, mixes anddispenses liquids in predetermined ratios without instrumentcalibration.

BACKGROUND OF THE INVENTION

There is a need for simplified apparatus capable of accurately measuringand/or mixing different liquids very precisely. The pipette is a commonlaboratory device for obtaining small samples of liquid which are to bediluted or mixed. Conventional pipettes have the disadvantage ofrequiring calibration and the further drawback of requiring timeconsuming, painstaking care in order to achieve accuracy. Moreover,there are inherent safety problems associated with the oral pipetting ofcertain solutions.

To avoid the necessity of having to use separate pipettes for picking upand dispensing different liquids, a dual-piston syringe was developedwhich has the capability of sequentially picking up and dispensing twoliquids. While this dual-piston syringe has the benefit of accuracy,precision and speed, it lacks the ability to effect mixing or dilutionof multiple liquids prior to the time they are dispensed from thesyringe.

Certain procedures require that multiple liquids be diluted or mixed inpredetermined ratios before being dispensed. Prior to the presentinvention there was no way of satisfactorily diluting or mixingdifferent liquids in a pipette. Thus, for a uniform mixture to bedispensed from a pipette it was first necessary to premix the liquids inthe separate container to obtain a mixture which was then drawn into apipette from which the mixture could be dispensed. This procedure wasboth time consuming and wasteful of materials. Furthermore, the requiredsequence of steps increased the opportunity for contamination of theliquids.

SUMMARY OF THE INVENTION

An object of the present invention is to provide an improved pipette.

Another object of the present invention is to provide a pipette capableof accurately and rapidly mixing precisely measured quantities ofdifferent liquids.

Still another object of the present invention is to provide a pipettewhich is capable of picking up multiple liquid samples in precise ratioand of completely mixing the liquids before they are dispensed.

A further object of the present invention is to provide a pipette whichcan be used without operator calibration and without pipetting error.

In accordance with the present invention plunger operated apparatushaving a casing with piston type plunger means inside the casing andmeans connected to the plunger means for moving the plunger meansaxially within the casing are provided. Cooperable plunger and casingshoulder means are provided for accurately regulating relative movementof the plunger means and casing to permit the sequential and separatepickup of different liquids by the apparatus, the mixing of thedifferent liquids within the apparatus and the dispensing of theresulting mixed liquids from the apparatus. The apparatus permitspredetermined ratios of liquids to be picked up and mixed accurately andrapidly to obtain a homogeneous mixture which can then be dispensed.

BRIEF DESCRIPTION OF THE DRAWINGS

Other and further objects, advantages and features of the invention willbe apparent to those skilled in the art from the following detaileddescription thereof, taken in conjunction with the accompanyingdrawings, in which:

FIG. 1 is a plan view of a pipette, in partial cross section, inaccordance with the present invention;

FIG. 2 is an enlarged view of the pin guide layout corresponding to thecooperable shoulder means present in FIG. 1 and further illustrated byFIGS. 3-10; and

FIGS. 3-10 are side views, partially broken away, of the pipette of FIG.1 illustrating in sequence various positions of the plunger keyed todifferent positions of the cooperable shoulder means and showing thepickup, mixing and dispensing of liquids from the tip of the pipette.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

The pipette apparatus of the present invention is characterized byhaving cooperable plunger and casing shoulder means which accuratelyregulates relative movement of the pipette plunger and casing to permitthe sequential and separate pickup of different liquids, the mixing ofthe different liquids within the apparatus and the dispensing of theresulting mixed liquids from the apparatus.

Turning now to FIG. 1 of the drawings, pipette 10 is illustrated ashaving a tapered tip 11 attached to one end of a generally cylindricalbarrel or casing 12, said casing being formed at the other end withshoulder means in the form of cutaway portions defining a pin guide 13.A plunger 14 extends coaxially into casing 12 and is connected to apiston 15. At its outer end plunger 14 is provided with shoulder meansin the form of a radially outwardly directed pin or detent member 28replaceably positioned in a suitable bore and adapted to coact with pinguide 13 in a manner to be described hereinafter.

It will be understood that the exact configuration of casing 12 is notcritical to the invention. In FIG. 1 casing 12 is shown having a taperedend portion 16 terminating in a reduced neck portion 18 to which taperedtip 11 is attached in a manner well known in the art. An enlargedcylindrical shoulder member 20 is attached to the casing 12 adjacent pinguide 13, said member being formed with a radially outwardly directedannular flange 22 adjacent the inner end thereof, which flange servesbasically to facilitate holding of the pipette in an individual's handwhile operating plunger 14. The described elements relating to casing 12extending from reduced neck portion 18 to enlarged shoulder member 20are well known elements of piston type prior art pipettes. These variouscomponent elements can be made from any suitable material, such asmetal, glass, rubber, or plastic.

Tapered tip 11 can be made to be removable and suitably attached byfriction, threaded means or the like to reduced neck portion 18 ofcasing 12. The tapered tip can also be made of any suitable material,such as metal, glass, rubber, or plastic, and can, if desired, bedisposable.

Plunger 14 is provided at its outer end with an enlarged head 24, saidplunger extending coaxially into casing 12 where it is operativelyconnected in known manner to piston 15. In a well known manner, outwardmovement of plunger 14 and piston 15, creates a vacuum inside casing 12,whereas inward movement of said plunger and piston creates pressure insaid casing. As hereinafter described, movement of plunger 14 and piston15 is constrained by coaction of pin 28 and pin guide 13. The shape ofpin guide 13 is best seen in the pin guide layout illustrated in FIG. 2.

Referring to FIG. 2, it will be seen that pin guide 13 is constructed tohave a number of different surface portions or notches 30 to 33 forregulating movement of pin 28. These surface portions or notches,together with pin 28 comprise cooperable shoulder means on casing 12 andplunger 14 defining positions to which pin 28 may be moved and therebycorresponding positions to which plunger 14 can be moved between itsoutermost position, represented by the outer surface of notch 33, andits innermost position represented by base line surface 34.

Ordinarily, pin 28 is maintained against an outer surface portion of pinguide 13 in one of the notches 30 to 33 by action of spring 35 (FIG. 1)inside casing 12. By pressing inwardly on head 24 of plunger 14 it ispossible to move pin 28, within the confines of pin guide 13, towardbase line surface 34 from positions in contact with the surfaces ofnotches 30, 31 and 32 and toward base line surface 36 from a position incontact with the outer surface of notch 33. The significance of thevarious notches 30 to 33 will be explained in greater detail inconnection with a description of FIGS. 3 through 10.

In FIGS. 3-10 the opposite end portions of pipette 10 are shown injuxtaposition in order to facilitate an understanding of the operationof the pipette. In FIG. 3 pin 28 is illustrated in a first position,being biased into contact with the outer surface of retaining notch 30near base line surface 34 of pin guide 13 by action of spring 35. Inthis position piston 15 is at essentially the innermost position incasing 12 in which it can be disposed under the constraints of thecoaction of pin 28 and pin guide 13. This is the position for plunger 14before any liquid is drawn up into tapered tip 11. By inserting taperedtip 11 in a liquid (not shown) while pin 28 rests within notch 30 of pinguide 13, and then manually rotating head 24, and thereby plunger 14,clockwise as viewed from the right in FIGS. 3 to 10, pin 28 moves intoregistry with notch 31 of pin guide 13 whereupon spring 35 moves plunger14 axially outwardly in casing 12 to the position thereof shown in FIG.4 wherein pin 28 engages the surface of notch 31. The outward plungermovement causes a vacuum to occur within tip 11, which vacuum causes aprecisely measured amount of liquid 38 to be drawn up into tip 11 asillustrated in FIG. 4.

Removal of tip 11 from the first liquid and insertion thereof into asecond liquid permits a precisely measured amount of the latter to alsobe drawn into tip 11. This is accomplished by further clockwise rotationof plunger 14 to position pin 28 in registry with notch 32, whereuponspring 35 moves plunger 14 outwardly to the position represented bycontact of pin 28 with the surface of notch 32 shown in FIG. 5. Suchoutward plunger movement causes the second liquid 40 to be drawn up intotip 11 as is also shown in FIG. 5.

Still further clockwise rotation of plunger 14 causes spring 35 to movepin 28 along the outer surface of guide 13 into contact with the outersurface of notch 33, while at the same time causing correspondingoutward movement of plunger 14 to the position of FIG. 6. If this lattermovement occurs while tip 11 is withdrawn from any body of liquid,liquids 38 and 40 will move inwardly as layers within tip 11, asillustrated in FIG. 6, and an air space will result in the outer end ofthe tapered tip 11 as shown.

Liquids 38 and 40, shown in FIGS. 5 and 6, are for all practicalpurposes separate liquid segments even at their interface. Thus, ifliquids 38 and 40 in FIG. 5 were dispensed or expelled from tapered tip11 mixing of the liquids would occur only after being dispensed.However, because of the coaction of pin 28 and guide 13 the presentinvention permits mixing of liquids to occur inside tip 11 in order thata homogeneous mixture of liquids can be dispensed from pipette 10. Themixing and dispensing of the liquids are described in connection withFIGS. 7 through 10.

Referring specifically to FIGS. 6, 7 and 8 it will be seen thatalternate application and release of axially inwardly directed digitalpressure on plunger head 24 against the bias of spring 35 causesreciprocating axial movement of plunger 14 as pin 28 moves intoalternate engagement with base line surface 36 and the outer surface ofnotch 33. Such plunger movement causes the liquids inside tip 11 to moveoutwardly within tip 11 to the position thereof shown in FIG. 8. Suchmovement causes the liquids to become subjected to extremely effectivevortex mixing, resulting in a uniform and homogenous mixture of saidliquids. The extent of mixing can be controlled by the number of timesplunger 14 is reciprocated as described. Moreover, the mixing action canbe as intense or violent as one desires depending upon the rapidity ofplunger reciprocation.

Upon completing the mixing of liquids inside tapered tip 11, dispensingthereof can be accomplished by counterclockwise rotation of plunger 14to the position illustrated in FIG. 9, wherein pin 28 is laterallyoffset from the base line surface 36, and then, by application ofdigital pressure to head 24, depressing plunger 14 against the bias ofspring 35 the full extent permitted by movement of pin 28 into contactwith base line surface 34 such plunger movement causes the preciselymeasured mixed liquids inside retaining tip 11 to be expelled ordispensed from tip 11 as the parts of pipette 10 are moved to thepositions thereof illustrated in FIG. 10.

Since pin guide 13 can be machined quite accurately with respect to anydesired configuration, pipettes can be made which eliminate anynecessity for calibration. Thus, uniform and consistent results can beachieved each time the pipette is used, eliminating pipetting errorstypically associated with the use of pipettes. The pipettes of thepresent invention also result in minimum sample preparation time due tothe absence of any need for priming the pipette, any need to calibratethe pipette, and the ease and precision with which the pipette can beoperated by simply manipulating plunger head 24 to achieve precisepositioning of plunger 14 and piston 15 by coaction of pin 28 with pinguide 13. Minimum sample preparation time also results from the factthat uniform and homogeneous mixing of liquids can be achieved insidethe pipette tip prior to the dispensing of the liquids.

As previously indicated, when the liquids are reciprocated axiallywithin the conical tip, extremely effective vortex mixing occurs. Themixing action illustrated by FIGS. 7-9 is in contrast to the segmentedmovement of liquids 38 and 40 illustrated in FIGS. 5 and 6 in which verylittle, if any, mixing occurs at the liquid interface. Thus, when thedual-piston syringe of the prior art draws up two liquids and thendispenses the liquids the liquids are dispensed or ejected in reverseorder of their pickup, such that the second liquid to be picked up isthe first liquid dispensed. It is because of the fact that the liquidsinside a dual-piston syringe are stratified that little, if any, mixingoccurs and whatever mixing does occur is nonuniform mixing at theinterface of the two liquids. In contrast, the pipette of the presentinvention achieves the desideratum of a uniform and homogeneous mixtureof liquids.

It will be appreciated that the apparatus illustrated in the drawings isa preferred embodiment of an invention designed primarily for operationusing thumb pressure on plunger head 24 against the bias of spring 35 tomove piston 14 from one position to another. Obviously, the apparatuscan be adapted for operation according to other convenient formats. Forexample, pin 28 can be elongated to function as a "shifting lever" tosimilarly move piston 14 from one position to another.

The pipette 10 can be made substantially contamination free by usingreplaceable tips and having all the mixing occurring within areplaceable tip. Obviously, pin guide 13 can be formed in a replaceableportion of casing 12 to provide for selective changing the volume,number of liquids to be picked up and the volumetric ratio of theliquids, within the capacity limitations of the pipette. Thus, aone-in-four dilution or one-in-fifty dilution can be readily achieveddepending upon the configuration of the pin guide. Differentproportions, meeting the exact specifications required for a particularoperation, can be obtained by selecting a casing portion formed with apin guide 13 capable of effecting the desired result. It will also beapparent to one skilled in the art that an alternative tointerchangeable pin guide means would be to provide shoulder meansforming one or more of the surfaces 30 to 33, which shoulder means isselectively moveable axially to alternative operation positions.

From the foregoing, it will be seen that this invention is well adaptedto attain all of the ends and objects hereinabove set forth, togetherwith other advantages which are obvious and inherent to the system.Apparatus of the present invention has the advantages of convenience,simplicity, relative inexpensiveness, positiveness, effectiveness,accuracy, and directness of action. The invention permits precisedilution of liquids or mixing to occur inside a pipette and can even beautomated.

Obviously, many other modifications and variations of the invention ashereinbefore set forth may be made without departing from the spirit andscope thereof.

What is claimed is:
 1. In a pipette or the like having a barrel providedat one end with a restricted opening, a piston within said barrel havinga plunger attached thereto and coaxially projecting from the other endof said barrel, the improvement which comprises cooperable shouldermeans on said barrel and plunger relatively movable to a plurality ofoperative positions, said shoulder means defining first and secondaxially spaced positions of said plunger with respect to said barrel andat least one third position of said plunger located intermediate saidfirst and second plunger positions, said shoulder means defining saidplunger positions at respectively different operative positions.
 2. Theimprovement of claim 1 wherein said shoulder means defines two axiallyspaced third plunger positions.
 3. The improvement of claim 1 whereinsaid first and second positions of said plunger are respectively fullyadvanced and retracted positions thereof and said cooperable shouldermeans, when in the operative positions defining said second plungerposition, also defining a fourth plunger position spaced from said firstposition and permitting reciprocating movement of said plunger betweensaid second and fourth positions.
 4. The improvement of claim 3 whichadditionally comprises means biasing said plunger axially toward saidsecond position.
 5. The improvement of claim 1 wherein the relativemovement of said shoulder means is rotary movement coaxial with saidplunger.
 6. The improvement of claim 1 wherein said cooperable shouldermeans comprises a detent member carried by said plunger and engageablewith surface portions of guide means carried by said barrel.
 7. Theimprovement of claim 6 wherein said guide means comprises a tubularmember coaxially surrounding said plunger and having cutaway portionsdefining said surface portions, and wherein said detent projectsradially from said plunger.
 8. A device for collecting, mixing anddispensing liquids which includes:an elongated chamber; a restrictedpassageway located at one end of said chamber adapted to accommodate thepassage of liquids into said chamber; a plunger operated piston memberforming a wall in said chamber moveable between a fully retracted pistonand an advanced position, the movement of said piston member in saidchamber being perpendicular to the cross-section of said chambercreating a force upon said restricted passageway and any liquids in saidpassageway which force is dependent upon the direction of movement ofsaid piston member; and guide means attached to said elongated chamber,said guide means comprising a tubular member coaxially surrounding andengaging detent means on said plunger for regulating the movement ofsaid plunger to at least four operative positions of the plungeroperated piston member, including the fully retracted position, theadvanced position and at least two intermediate positions.
 9. The deviceof claim 8 which additionally comprises means for biasing said plungeroperated piston member axially toward said fully retracted position. 10.The method of collecting, mixing and dispensing liquids whichincludes:drawing a first liquid through a restricted inlet passagewaylocated at one end of an elongated chamber to a first position insidesaid elongated chamber; drawing the first liquid to a second positioninside said elongated chamber while simultaneously drawing a secondliquid through the inlet passageway into said elongated chamber suchthat the first and second liquids form contiguous, but substantiallyseparate liquid layers inside said elongated chamber; moving said firstand second contiguous liquid layers longitudinally within said elongatedchamber and away from said inlet passageway so as to form an air spacebetween said inlet passageway and the second liquid; causingreciprocating movement of the first and second liquids entirely withinthe elongated chamber to cause mixing of the first and second liquids;and then dispensing the resulting mixed liquids from the restrictedinlet passageway of said elongated chamber.